X-ray diagnostic apparatus

ABSTRACT

An X-ray diagnostic apparatus comprises: an X-ray detector including a first detector and a second detector capable of simultaneously detecting X-rays irradiated from an X-ray tube; and processing circuitry configured to correct, by using information of a second image that is based on an output from the second detector, a first image that is based on an output from the first detector.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2017-49482, filed on Mar. 15, 2017; theentire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to an X-ray diagnosticapparatus.

BACKGROUND

Conventionally, during medical examinations using X-ray diagnosticapparatuses, a small region of interest may be observed with a highresolution in some situations. For this reason, a known X-ray diagnosticapparatus is provided with detectors including both a first detectorthat has a large field of view (FOV) part using a Thin Film Transistor(TFT) array and a second detector that uses a Complementary Metal OxideSemiconductor (CMOS) and has a smaller FOV and a smaller pixel pitchthan those of the first detector.

With such a type of X-ray diagnostic apparatus, a technique is known bywhich the detector in use is switched between the first detector and thesecond detector depending on purposes, so as to display one selectedfrom between a first image generated from an X-ray signal output by thefirst detector and a second image generated from an X-ray signal outputby the second detector.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating an exemplary configuration of anX-ray diagnostic apparatus according to a first embodiment;

FIG. 2 is a block diagram illustrating an exemplary configuration of anX-ray detector according to the first embodiment;

FIG. 3 is a diagram for explaining operations in an X-ray imageacquiring process performed by a conventional X-ray diagnosticapparatus;

FIG. 4 is a block diagram illustrating an exemplary configuration of anX-ray image acquirer according to the first embodiment;

FIG. 5 is a flowchart illustrating a processing procedure performed bythe X-ray image acquirer according to the first embodiment;

FIG. 6A is a diagram for explaining a second embodiment;

FIG. 6B is another diagram for explaining the second embodiment;

FIG. 6C is yet another diagram for explaining the second embodiment;

FIG. 7 is a block diagram illustrating an exemplary configuration of anX-ray image acquirer according to the second embodiment; and

FIG. 8 is a flowchart illustrating a processing procedure performed bythe X-ray image acquirer according to the second embodiment.

DETAILED DESCRIPTION

An X-ray diagnostic apparatus comprises an X-ray detector and processingcircuitry. The X-ray detector includes a first detector and a seconddetector capable of simultaneously detecting X-rays irradiated from anX-ray tube. The processing circuitry is configured to correct, by usinginformation of a second image that is based on an output from the seconddetector, a first image that is based on an output from the firstdetector.

Exemplary embodiments of the X-ray diagnostic apparatus will beexplained below, with reference to the drawings Embodiments are notlimited to the embodiments described below. Further, the contents ofeach of the embodiments are, in principle, similarly applicable to anyother embodiment.

FIG. 1 is a block diagram illustrating an exemplary configuration of anX-ray diagnostic apparatus 100 according to a first embodiment. Asillustrated in FIG. 1, the X-ray diagnostic apparatus 100 according tothe first embodiment includes a catheter bed 101, a holder 102, an X-rayhigh-voltage generator 107, a holder controller 108, a monitor 109, anX-ray image acquirer 110, an X-ray detector (Flat Panel Detector)controller 120, and an input interface 130.

The catheter bed 101 is movable in a vertical direction and a horizontaldirection. A subject P is placed on the catheter bed 101. The holder 102is configured to be rotatable on a Z-axis in the direction indicatedwith the arrow R and is configured to hold an X-ray source 103 and anX-ray detector 106 facing each other.

The X-ray source 103 includes an X-ray tube 103 a configured toirradiate X-rays and an aperture (also referred to as a collimator) andradiation quality adjusting filter 103 b used for the purpose ofreducing the radiation exposure amount for the subject P and improvingimage quality of image data.

The X-ray detector (which may be referred to as a Flat Panel Detector[FPD]) 106 is configured to detect X-rays that were irradiated from theX-ray source 103 and have passed through the subject P. The X-raydetector 106 includes a first detector and a second detector that arecapable of simultaneously detecting X-rays irradiated from the X-raysource 103. In the following sections, the X-ray detector 106 accordingto the first embodiment will be explained, with reference to FIG. 2.FIG. 2 is a block diagram illustrating an exemplary configuration of theX-ray detector 106 according to the first embodiment.

For example, as illustrated in FIG. 2, the X-ray detector 106 includes afirst photodetector 106 a, a second photodetector 106 b, and ascintillator 106 c. The first photodetector 106 a and the scintillator106 c constitute a first detector 106 d (also referred to as a firstFPD), and the second photodetector 106 b and the scintillator 106 cconstitute a second detector 106 e (also referred to as a second FED).The first FED is one example of the first detector. The second FED isone example of the second detector. In FIG. 2, the scintillator 106 c isarranged so as to be sandwiched between the first photodetector 106 aand the second photodetector 106 b.

The scintillator 106 c is configured to convert the F-rays irradiatedfrom the X-ray source 103 into light. The first photodetector 106 aincludes a two-dimensional image sensor using a Thin Film Transistor(TFT) array formed by using amorphous silicon, for example, and isconfigured to detect the light converted from X-rays by the scintillator106 c and to output an electrical signal. The second photodetector 106 bincludes a two-dimensional image sensor using a Complementary MetalOxide Semiconductor (CMOS) transistor, for example, and is configured todetect the light converted from X-rays by the scintillator 106 c and tooutput an electrical signal. The electrical signals output by the firstphotodetector 106 a and the second photodetector 106 b may be referredto as X-ray signals.

In this manner, the scintillator 106 c is shared by the firstphotodetector 106 a and the second photodetector 106 b. In other words,the X-ray detector 106 includes: the scintillator 106 c configured toconvert the X-rays irradiated from the X-ray source 103 into the light;and the first photodetector 106 a and the second photodetector 106 bthat share the scintillator 106 c and are configured to detect the lightconverted by the scintillator 106 c and to output the electricalsignals. Further, the first photodetector 106 a and the secondphotodetector 106 b are configured to output the electrical signals as aresult of simultaneously detecting the light converted from X-rays bythe scintillator 106 c.

Further, as illustrated in FIG. 2, the first photodetector 106 a and thesecond photodetector 106 b each include a plurality of elements servingas structural units of pixels. Each of the elements is configured toconvert a fluorescent image obtained as a result of incidence of anX-ray, into an electrical signal and to store the electrical signal intoa photodiode (PD). FIG. 2 illustrates an example in which the firstphotodetector 106 a includes eight elements, and the secondphotodetector 106 b includes eight elements.

In this situation, the pixel pitch of the elements of the secondphotodetector 106 b is smaller than the pixel pitch of the elements ofthe first photodetector 106 a. In the example illustrated in FIG. 2, thepixel pitch of the elements of the first photodetector 106 a correspondsto the pixel pitch of two elements of the second photodetector 106 b. Inother words, the resolution of the second photodetector 106 b is higherthan that of the first photodetector 106 a. Further, as illustrated inFIG. 2, the size of the FOV of the first photodetector 106 a is largerthan that of the second photodetector 106 b.

Further, the maximum incident X-ray amount of the second photodetector106 b using the CMOS tends to be smaller than that of the firstphotodetector 106 a using amorphous silicon. For this reason, with thesecond photodetector 106 b, when an attempt is made to acquire X-rayimage data having a high Signal-to-Noise (S/N) ratio by radiating X-raysof a high dose, it may not be possible to do so in some situations.

Further, a residual component resulting from incident X-ray of thesecond photodetector 106 b is smaller than that of the firstphotodetector 106 a. In the first photodetector 106 a, within thephotodiodes, generated electric charges are trapped at a trap level onthe inside thereof. In contrast, in the second photodetector 106 b, dueto the nature of the CMOS, not many of the electric charges generated inthe photodiodes are trapped. In other words, an electrical signalresidual component of the second optical detector 106 b is smaller thanthat of the first optical detector 106 a.

Returning to the description of FIG. 1, the X-ray detector controller120 is configured to control timing with which the electrical signalsare read by the X-ray detector 106. Further, the X-ray detectorcontroller 120 is configured to acquire the electrical signals from theX-ray detector 106, to generate image data from the acquired electricalsignals, and to output the image data to the X-ray image acquirer 110.In this situation, the X-ray detector controller 120 acquires theelectrical signal output by the first FPD, generates first image data(which may be referred to as a first FPD image or a first image) fromthe acquired electrical signal, and outputs the first image data to theX-ray image acquirer 110. Further, the X-ray detector controller 120acquires the electrical signal output by the second FPD, generatessecond image data (which may be referred to as a second FPD image or asecond image) from the acquired electrical signal, and outputs thesecond image data to the X-ray image acquirer 110.

The X-ray image acquirer 110 is configured to acquire the image dataoutput by the X-ray detector controller 120 by controlling the holdercontroller 108 and the X-ray high-voltage generator 107 and to furtherperform an image processing process. In this situation, the X-ray imageacquirer 110 acquires the image data from the first FPD and from thesecond F0D, with substantially the same timing. Details of the X-rayimage acquirer 110 will be explained later.

The X-ray high-voltage generator 107 is configured to supply highvoltage to the X-ray tube 103 a. Under the control of the X-ray imageacquirer 110, the holder controller 108 is configured to controlrotations of the holder 102, and the like. The monitor 109 is configuredto display an X-ray image generated by the X-ray image acquirer 110 andthe like. The monitor 109 may be structured with a plurality of submonitors or may be a large-screen monitor capable of arbitrarilydividing the display region thereof according to an instruction from theoperator. Further, when the monitor 109 includes the plurality of submonitors, the display region of each of the sub monitors may arbitrarilybe divided according to an instruction from the operator. The inputinterface 130 is configured by using a keyboard, a control panel, a footswitch, and/or the like and is configured to receive inputs of varioustypes of operations performed on the X-ray diagnostic apparatus 100 fromthe operator.

An overall configuration of the X-ray diagnostic apparatus 100 accordingto the first embodiment has thus been explained. Structured as describedabove, the X-ray diagnostic apparatus 100 according to the firstembodiment is configured to acquire the X-ray signals output by theX-ray detector 106. Further, the X-ray diagnostic apparatus 100 isconfigured to cause the monitor 109 to display an image generated fromthe acquired X-ray signals. For example, the X-ray diagnostic apparatus100 causes the monitor 109 to display an image set by the operator inaccordance with a clinical site. For example, the X-ray diagnosticapparatus 100 causes the monitor 109 to display images by switchingbetween the first image and the second image according to an instructionfrom the operator.

In such an X-ray diagnostic apparatus, in some situations, the secondFPD that is on the second photodetector 106 b side and has a higherresolution and a smaller FOV may be used during a treatment manipulationor the like, for a relatively long period of time. FIG. 3 is a diagramfor explaining operations in an X-ray image acquiring process performedby a conventional X-ray diagnostic apparatus 100.

The left section of FIG. 3 illustrates an example in which an X-rayradiation region is set to be equal to the size of the FOV of the secondFPD. In that situation, the X-ray diagnostic apparatus 100 acquires theX-ray signal output by the second FPD and causes the monitor 109 todisplay the second image as an image on the user's acquisitionintended-side. In this situation also, the X-ray diagnostic apparatus100 acquires the X-ray signal output by the first FPD and generates thefirst image. Rendered in the first image are a FOV having an equal sizeto the size of the FOV of the second FPD and X-ray collimator blades inthe surroundings of the FOV.

Subsequently, the image displayed on the monitor 109 is changed from thesecond image to the first image. The right section of FIG. 3 illustratesan example in which the X-ray radiation region is changed to have thesize of the FOV of the first FPD. In that situation, the X-raydiagnostic apparatus 100 acquires the X-ray signal output by the firstFPD and causes the monitor 109 to display the first images an image onthe user's acquisition intended-side. In this situation also, the X-raydiagnostic apparatus 100 acquires the X-ray signal output by the secondFPD and generates the second image. Rendered in the second image is aFOV having an equal size to the size of the FOV of the second FPD.

In this situation, for example, when a fluoroscopy/imaging manipulationis performed by using the second FPD for a long period time, in theregion of the first FPD corresponding to the size of the FOV of thesecond FPD, offset components of the image are changed, due to thegenerated electric charges trapped at the trap level being read withtiming different from expected timing. This change in the offsetcomponents is caused because, when powerful X-rays have been irradiatedonto the first FPD for a certain period of time, the generated electriccharges are trapped at the trap level on the inside of the photodiodesconfigured to detect the light, and the electric charges are released byenergy of heat or the like and are read as being mixed with subsequentX-ray signals. In other words, in the first FPD, the electric chargesare read as being mixed with the X-ray signals, with undesirable timing.For this reason, in a fluoroscopic image having a larger FOV obtainedthe first FPD after using the second FPD for a long period of time, anartifact exhibiting something like a baked pattern occurs, due to anelectrical signal residual component of the first photodetector 106 a.This artifact may appear approximately 10 seconds, for example. Incontrast, no such artifact appears on the outside of the size of the FOVof the second FPD to which incidence of X-rays is blocked by theaperture blades of the X-ray collimator.

Accordingly, when the first FPD, which is on the first photodetector 106a side, that has a larger FOV is selected for the subsequentmanipulation, an image is obtained in which a pattern is baked inaccordance with the difference in the radiation history on the first FPDmade by the X-ray collimator. For example, in some situations, afluoroscopic image obtained by the first FPD may exhibit a pattern inwhich the shapes of the blades of the X-ray collimator are baked. Thefirst image illustrated in the upper right section of FIG. 3 indicatesthat, when an image acquisition is performed by using the second FPD,and subsequently another image acquisition is performed by switching tothe first FPD, an artifact having the shapes of the blades of the X-raycollimator is exhibited. The baked pattern in the first image describedabove occurring due to the electrical signal residual component willhereinafter be referred to as a ghost artifact. In other words, theghost artifact occurs due to the electrical signal residual component ofthe first photodetector 106 a.

In the CMOS, due to the nature thereof, not many of the electric chargesgenerated in the photodiodes are trapped. Accordingly, ghost artifactsare much less likely to occur in the CMOS, compared to those in theamorphous silicon TFT used in the first FPD. For this reason, whencorrecting the region of the first FPD image corresponding to the FOV ofthe second FPD, it is acceptable to refer to the second FPD image, whichis free of changes made by an X-ray dose history.

For this reason, when causing the monitor 109 to display the first imagegenerated from the electrical signal output by the first photodetector106 a, the X-ray diagnostic apparatus 100 according to the firstembodiment corrects first image by using information of the second imagegenerated from the electrical signal output by the second photodetector106 b. This correcting process is performed by the X-ray image acquirer110. In the following sections, details of the correcting processperformed by the X-ray image acquirer 110 will be explained, withreference to FIG. 4. The X-ray image acquirer 110 is an example of acontroller.

FIG. 4 is a block diagram illustrating an exemplary configuration of theX-ray image acquirer 110 according to the first embodiment. Forconvenience of explanation, FIG. 4 also illustrates the X-ray source103, the X-ray detector 100, the X-ray detector controller 120, themonitor 109, and the input interface 130. FIG. 2 illustrates the examplein which the X-ray detector 106 includes the first photodetector 106 a,the second photodetector 106 b, and the scintillator 106 c. However, inactuality, as illustrated in FIG. 4, the X-ray detector 106 alsoincludes video signal amplification circuitry and analog to digital(A/D) conversion circuitry. The second photodetector 106 b may beconfigured so that each of the elements includes A/D conversioncircuitry and video signal amplification circuitry. In that situation,the second photodetector 106 b is configured to convert a storedelectrical signal into a digital signal, to subsequently amplify thedigital signal, and to output the amplified digital signal. With thisarrangement, the second photodetector 106 b is able to output theelectrical signal in which noise is decreased. As illustrated in FIG. 4,in the X-ray detector 106, the first FPD is provided on the X-ray source103 side, relative to the second FPD.

Further, the X-ray detector 106 includes drive control circuitry 106 fand video signal processing circuitry 106 g. The drive control circuitry106 f is configured to control driving timing of the first photodetector106 a and the second photodetector 106 b under the control of the X-raydetector controller 120. The video signal processing circuitry 106 g isconfigured to acquire an electrical signal output from the firstphotodetector 106 a, to output the acquired electrical signal to theX-ray detector controller 120, to acquire an electrical signal outputfrom the second photodetector 106 b, and to output the acquiredelectrical signal to the X-ray detector controller 120.

With reference to FIG. 4, the example is explained in which the transferof images from the X-ray detector controller 120 to the X-ray imageacquirer 110 uses a parallel scheme where data lines are provided forthe first image and for the second image; however, embodiments are notlimited to this example For instance, the transfer of the images fromthe X-ray detector controller 120 to the X-ray image acquirer 110 mayuse a serial scheme where a data line is shared between the first imageand the second image.

The X-ray image acquirer 110 according to the first embodiment includes,as illustrated in FIG. 4, FPC control circuitry 201, image processingcircuitry 202, a disk 203, a disk 204, and ghost artifact correctingcircuitry 210.

The FFD control circuitry 201 is configured to control, via the X-raydetector controller 120, timing with which the electrical signals areread by the X-ray detector 106. The image processing circuitry 202 isconfigured to perform an image processing process on the image dataoutput by the X-ray detector controller 120. The disk 203 is configuredto store X-ray images therein. For example, the disk 203 is configuredwith a Hard Disk Drive (HDD) and stores the second image therein. Thedisk 204 is configured to store X-ray images therein. For example, thedisk 204 is configured with an HDD and stores the first image therein.The input interface 130 is configured to receive an instruction from theoperator and to control a switch C. In this situation, when the inputinterface 130 moves the switch C to side “a”, the image processingcircuitry 202 displays the first image. In contrast, when the inputinterface 130 moves the switch C to side “b”, the image processingcircuits 202 displays the second image. With reference to FIG. 4, theexample is explained in which the X-ray image acquirer 110 includes thedisk 203 for the second image and the disk 204 for the first image;however, another arrangement is also acceptable in which the first imageand the second image share a single disk.

The ghost artifact correcting circuitry 220 is configured to determinewhether a ghost artifact has occurred or not. For example, the ghostartifact correcting circuitry 210 calculates the difference valuebetween a pixel value obtained by multiplying a pixel value of thesecond image by a coefficient corresponding to a sensitivity ratiobetween the first photodetector 106 a and the second photodetector 106 band a pixel value of the first image and, when the calculated differencevalue is equal to or larger than a set threshold value, the ghostartifact correcting circuitry 210 determines that a ghost artifact hasoccurred. In this situation, the ghost artifact correcting circuitry 210performs the determining process described below, on ice pixels in a FOVregion of the first FPD corresponding to the size of the FOV of thesecond FPD. In that situation, in the X-ray image acquirer 110, a switchA illustrated in FIG. 4 is moved to side “a”, so that the pi in the FOVregion of the first FPD corresponding to the size of the FOV of thesecond FPD are input to the ghost artifact correcting circuitry 210.After that, the ghost artifact correcting circuitry 210 performs thedetermining process. Further, in the X-ray image acquirer 110, when theprocessed region of the first FOP image is out of the size of the FOV ofthe second FPD, the switch A is moved to side “b”, so that the originalfirst FPD image is input to the image processing circuitry 202 withoutgoing through the determining process. The ghost artifact correctingcircuitry 210 includes, for example, FPD gain conversion coefficientstorage circuitry 211, threshold value storage circuitry 212, re-sizingcircuitry 213, determining circuitry 214, and multiplying circuitry 215.

The FPD gain conversion coefficient storage circuitry 211 is configuredto store therein the coefficient corresponding to the sensitivity ratiobetween the first photodetector 106 a and the second photodetector 106b. The threshold value storage circuitry 212 is configured to storetherein the threshold value used by the determining circuitry 214.

The multiplying circuitry 215 is configured to read the coefficientstored in the FPD gain conversion coefficient storage circuitry 211 andto multiply the second image by the read coefficient. By multiplying thesecond FOD image, which is free of changes made by an X-ray dosehistory, by the coefficient corresponding to the sensitivity ratiobetween the first photodetector 106 a and the second photodetector 106b, the multiplying circuitry 215 calculates pixel values of the firstFPD image in a state that is free of changes in the X-ray dose history.The multiplying circuitry 215 then forwards the second image after themultiplication, to the re-sizing circuitry 213.

When the pixel value of the first image is compared with the pixel valueof the second image, the re-sizing circuitry 213 is configured tocorrect the pixel pitch of the second image. The second FPD has asmaller pixel pitch and a higher resolution than the first FPD. For thisreason, to compare pixel values in the same position between the firstimage and the second image, the re-sizing circuitry 213 makes acorrection so that the pixel pitch of the second FPD image becomes equalto the pixel pitch of the first FPD image. The re-sizing circuitry 213forwards the second image after the re-sizing process, to thedetermining circuitry 214.

The determining circuitry 214 is configured to calculate the differencevalue between the pixel value obtained by multiplying the pixel value ofthe second image by the coefficient corresponding to the sensitivityratio between the first photodetector 106 a and the second photodetector106 b and the pixel value of the first image and determines whether ornot the difference value is larger than the set threshold value. Inother words, the determining circuitry 214 calculates the differencevalue between the pixel value of the first FPD image in a state that isfree of changes in the X-ray dose history and the actual pixel value ofthe first FPD image and determines whether or not the calculateddifference value is larger than the set threshold value. Further, whenthe difference between the pixel value obtained by multiplying the pixelvalue of the second image by the coefficient corresponding to thesensitivity ratio between the first photodetector 106 a and the secondphotodetector 106 b and the pixel value of the first image is equal toor larger than the threshold value, the determining circuitry 214determines that an artifact has occurred. In that situation, the switchB is moved to side “a”, so that the pixel value obtained from the secondFPD image replaces the pixel value obtained from the first FPD image andis input to the image processing circuitry 202.

The image processing circuitry 202 is configured to separately applynecessary image processing processes to the first FPD image and to storethe first FPD image into the disk 204, and to also cause the monitor 109to display the first FPD image. In this situation, because the first FPDimage is designated by the user through the input interface 130, as animage currently desired by the user to be displayed, the switch C ismoved to side “a”. In contrast, when a manipulation using the second FPDis selected by the user through the input interface 130, the imageprocessing circuitry 202 causes the monitor 109 to display the secondFPD image. In that situation, the switch C is moved to side “b”. In thepresent embodiment, the example is explained in which the ghost artifactis exhibited as the blades of the X-ray collimator; however, embodimentsare not limited to this example. Further, as long as the positions ofthe blades of the X-ray collimator are within the size of the FOV of thesecond FPD, it is possible to similarly correct ghost artifacts of theblades.

FIG. 5 is a flowchart illustrating a processing procedure performed bythe X-ray image acquirer 110 according to the first embodiment. FIG. 5presents the flowchart explaining overall operations of the X-ray imageacquirer 110, and the following sections will explain to which steps inthe flowchart, the constituent elements thereof correspond. Thefollowing explanation is based on the assumption that the processesillustrated in FIG. 5 are performed in real time when a change to thefirst image is received at the time of acquiring the second image.

Step S101 is a step implemented by the X-ray image acquirer 110. At stepS101, the X-ray image acquirer 110 determines whether or not theprocessed region of the first image is within the size of the FOV of thesecond FPD. In this situation, when it is determined that the processedregion of the first image is not within the size of the FOV of thesecond FPD (step S101: No), the X-ray image acquirer 110 ends theprocess. On the contrary, when it is determined that the processedregion of the first image is within the size of the FOV of the secondFPD (step S101: Yes), the X-ray image acquirer 110 proceeds to stepS102.

Step S102 is a step implemented by the multiplying circuitry 215included in the ghost artifact correcting circuitry 210. At step S102,the multiplying circuitry 215 multiplies the second image by thecoefficient.

Step S103 is a step implemented by the re-sizing circuitry 213 includedin the ghost artifact correcting circuitry 210. At step S103, there-sizing circuitry re-sizes the second image. In other words, there-sizing circuitry 213 enlarges the second image so as to arrange thepixel pitch of the second image to be equal to the pixel pitch of thefirst image.

Step S104 is a step implemented by the determining circuitry 214included in the ghost artifact correcting circuitry 210. At step S104,the determining circuitry 214 calculates the difference value betweenthe pixel value of the second image and the pixel value of the firstimage.

Step S105 is a step implemented by the determining circuitry 214included in the ghost artifact correcting circuitry 210. At step S105,the determining circuitry 214 determines whether or not the differencevalue exceeds the threshold value. In this situation, when it isdetermined that the difference value does not exceed the threshold value(step S105: No), the determining circuitry 214 ends the process. On thecontrary, when it is determined that the difference value exceeds thethreshold value (step S105: Yes), the determining circuitry 214 proceedsto step S106.

Step S106 is a step implemented by the image processing circuitry 202included in the X-ray image acquirer 110. At step S106, the imageprocessing circuitry 202 corrects the first image by using the pixelvalue obtained from the second image.

As explained above, in the first embodiment, the electrical signalresidual component of the second photodetector 106 b is smaller thanthat of the first photodetector 106 a. In other words, no artifact dueto the electrical signal residual component is caused in the secondphotodetector 106 b. Further, in the first embodiment, in the situationwhere an artifact due to an electrical signal residual component occursin the first image, when the image displayed on the monitor 109 ischanged from the second image to the first image, the X-ray imageacquirer 110 corrects the first image by using the pixel value obtainedfrom the second image. As a result, according to the first embodiment,for example, it is possible to provide an image free of the occurrenceof ghost artifacts.

In the first embodiment above, the example is explained in which thesecond photodetector 106 b includes the two-dimensional image sensorusing the CMOS transistor; however, embodiments are not limited to thisexample. For instance, as the image sensor of the second photodetector106 b, it is acceptable to use amorphous silicon having a characteristicwhere fewer electric charges generated in the photodiode are trapped.

In the first embodiment above, the example is explained in which thecorrection is made by replacing the pixel value obtained from the firstFPD image with the pixel value obtained from the second FPD image;however, embodiments are not limited to this example. For instance, itis also acceptable to correct the pixel value obtained from the firstFPD image by using a correction value based on the pixel value obtainedfrom the second FPD image. In that situation, the first FPD image andthe second FPD image are input to the image processing circuitry 202. Inthis situation, when an artifact occurs in the first FFD image, thepixel value of the second FPD image input to the image processingcircuitry 202 corresponds to the pixel value of the first FFD imagewithout the occurrence of artifacts. Accordingly, the image processingcircuitry 202 calculates a correction value based on the pixel value ofthe second FPD image and the pixel value of the first FPD image. Forinstance, the image processing circuitry 202 corrects at least one ofthe pixel value of the second FPD image and the pixel value of the firstFPD image corresponding to sensitivity of the first photodetector 106 aand the second photodetector 106 b. And the image processing circuitry202 calculates a value obtained by subtracting a pixel value of thecorrected first FPD image from a pixel value of the corrected second FPDimage, as a correction value. After that, the image processing circuitry202 corrects the first FPD image by subtracting the calculatedcorrection value from the pixel value of the first FPD image. Thus, theimage processing circuitry 202 corrects residual component of the firstimage.

In the first embodiment, the example is explained in which, in thesituation where an artifact due to an electrical signal residualcomponent occurs in the first image, when the image displayed on themonitor 109 is changed from the second image to the first image, thefirst image is corrected by using the pixel value obtained from thesecond image. Incidentally, the X-ray diagnostic apparatus 100 may, insome situations, carry out a Digital Subtraction Angiography (DSA)imaging process with a FOV slightly larger than the second FPD, by usingthe first PD.

In that situation, when a motion artifact occurs due to a movement ofthe subject between the time of acquiring a mask image and the time ofacquiring a contrast image during the DSA manipulation, thecorresponding pixels shift between the mask image and the contrastimage. FIGS. 6A, 6B, and 6C are diagrams for explaining a secondembodiment.

FIGS. 6A, 6B, and 6C illustrate an example in which the first FPD imagewas designated by the user through the input interface 130, and theoperator has performed DSA manipulations while looking at the firstimage. FIG. 6A illustrates the X-ray source 103 and the X-ray detector106. In that situation, the first FPD and the second FPD each output anelectrical signal.

FIG. 6B illustrates a mask image and a contrast image generated from theelectrical signal output by the first FED. In this situation, when apixel shift amount between the mask image and the contrast image iscalculated, it may not be possible to achieve a sufficient level ofprecision for the correction in some situations, because the size ofeach pixel to be used is too large.

In this regard, as illustrated in FIG. 6C, when the pixel shift amountbetween the mask image and the contrast image is calculated, by usingthe second image having a smaller pixel size, it is possible toaccurately measure the shift between the mask image and the contrastimage. It is therefore possible to calculate the pixel shift amount moreaccurately. Accordingly, in the second embodiment, an example will beexplained in which, when the DSA manipulations have been performed whilethe first FPD image is designated, a motion artifact occurring betweenthe mask image and the contrast image is corrected by using the secondFED image.

Except that an X-ray image acquirer 110 a has functions different fromthose of the X-ray image acquirer 110 according to the first embodiment,an overall configuration of the X-ray diagnostic apparatus 100 accordingto the second embodiment is the same as the exemplary configurationillustrated in FIG. 1. Thus, explanation thereof will be omitted. TheX-ray image acquirer 110 a is an example of controller. FIG. 7 is ablock diagram illustrating an exemplary configuration of the X-ray imageacquirer 110 a according to the second embodiment. For convenience ofexplanation, FIG. 7 also illustrates the X-ray source 103, the X-raydetector 106, the X-ray detector controller 120, the monitor 109, andthe input interface 130. As illustrated in FIG. 7, in the X-ray detector106, the first FPD is provided on the X-ray source 103 side, relative tothe second FPD.

With reference to FIG. 7, the example is explained in which the transferof images from the X-ray detector controller 120 to the X-ray imageacquirer 110 a uses a parallel scheme where data lines are provided forthe first image and for the second image; however, embodiments are notlimited to this example. For instance, the transfer of the images fromthe X-ray detector controller 120 to the X-ray image acquirer 110 a mayuse a serial scheme where a data line is shared between the first imageand the second image.

The X-ray image acquirer 110 a according to the second embodimentincludes, as illustrated in FIG. 7, the FPD control circuitry 201, thedisk 203, the disk 204, UI controlling circuitry 205, and motionartifact correcting circuitry 220.

The FPD control circuitry 201 is configured to control, via the X-raydetector controller 120, timing with which the electrical signals areread by the X-ray detector 106. The disk 203 is configured to storeX-ray images therein. For example, the disk 203 is configured with anHOD and stores the second image therein. The disk 204 is configured tostore X-ray images therein. For example, the disk 204 is configured withan HDD and stores the first image therein. With reference to FIG. 7, theexample is explained in which the X-ray image acquirer 110 a includesthe disk 203 for the second image and the disk 204 for the first image;however, another arrangement is also acceptable in which the first imageand the second image share a single disk.

The input interface 130 is configured to receive instructions from theoperator and to forward the received instructions to the UI controllingcircuitry 205. The UI controlling circuitry 205 is configured to receivean instruction from the input interface 130 indicating that a motionartifact correcting process should be performed, and to cause the motionartifact correcting circuitry 220 to perform the motion artifactcorrecting process.

When the first image is to be displayed on the monitor 109, the motionartifact correcting circuitry 220 is configured to calculate a shiftamount by using the second image and to correct the first image by usingthe calculated shift amount. In that situation, in the X-ray imageacquirer 110 a, a pixel shift on/off switch illustrated in FIG. 7 ismoved to side “b” by the UI controlling circuitry 205 that has receiveda user command from the input interface 130. The motion artifactcorrecting circuitry 220 includes re-sizing coefficient storagecircuitry 221, pixel shift amount calculating circuitry 222, pixel shiftamount applying circuitry 223, image processing circuitry 224, andre-sizing circuitry 225.

The re-sizing coefficient storage circuitry 221 is configured to storetherein coefficients corresponding to sizes of the FOV. The pixel shiftamount calculating circuitry 222 is configured to calculate the shiftamount by using the second image. For example, because the second FEDimage is also input to the X-ray image acquirer 110 a at the same time,the pixel shift amount calculating circuitry 222 calculates a movementof the subject with a smaller pixel pitch and a higher level ofprecision, by using the second FED image. More specifically, the pixelshift amount calculating circuitry 222 calculates the shift amount byusing the second image acquired at the time of the acquisition of themask image and the second image obtained at the time of the acquisitionof the contrast image.

The re-sizing circuitry 225 is configured to calculate the shift amountby making a correction by multiplying the pixel pitch of the secondimage by a coefficient corresponding to the size of the FOV. Forexample, the first image and the second image have mutually-differentpixel pitches. For this reason, when a shift amount calculated by thepixel shift amount calculating circuitry 222 is applied to the first FPDimage, it is necessary to correct the difference in the image sizecaused by the difference in the pixel pitch between the first image andthe second image. Accordingly, the re-sizing circuitry 225 calculatesthe shift amount in which the difference in the pixel pitch has beencorrected, by performing the multiplying process using the coefficientcorresponding to the selected size of the FOV.

The pixel shift amount applying circuitry 223 applies the calculatedshift amount to the first image. For example, the pixel shift amountapplying circuitry 223 corrects either the mask image or the contrastimage of the first image, by using the calculated shift amount. In thissituation, although the size of the FOV in the first FPD image is largerthan the size of the FOV of the second FPD, a value calculated for acenter part may be used as the shift amount, and it is acceptable forthe pixel shift amount applying circuitry 223 to apply the calculatedshift amount to perimeter parts as well without any modification.Alternatively, it is also acceptable for the pixel shift amount applyingcircuitry 223 to approximate a shift amount on the outside of the FOV ofthe second FPD on the basis of shift amount transition characteristicsobtained from an image center part within the FOV of the second FPD andto apply the approximated shift amount on the outside of the FOV of thesecond FPD to the first image.

The image processing circuitry 224 is configured to cause the monitor109 to display images. For example, in the situation where the DSAmanipulations are performed while the operator is looking at the firstimage, when the first image is to be displayed, the image processingcircuitry 224 causes the monitor 109 to display the first image in whichmotion artifacts have been corrected by using the second image. When thesecond image is to be displayed, the image processing circuitry 224reads the second image from the disk 203 and causes the monitor 109 todisplay the read second image.

FIG. 8 is a flowchart illustrating a processing procedure performed bythe X-ray image acquirer 110 a according to the second embodiment. FIG.8 presents the flowchart explaining overall operations of the X-rayimage acquirer 110 a, and the following sections will explain to whichsteps in the flowchart, the constituent elements thereof correspond. Theprocedure will be explained on the assumption that the processesillustrated in FIG. 8 are performed after the mask image and thecontrast image are acquired through DSA manipulations.

Step S201 is a step implemented by the UI controlling circuitry 205. Atstep S201, the UI controlling circuitry 205 determines whether or not amotion artifact correcting process has been received. In this situation,when it is determined that no motion artifact correcting process hasbeen received (step S201: No), the UI controlling circuitry 205repeatedly performs the process at step S201. On the contrary, when itis determined that a motion artifact correcting process has beenreceived (step S201: Yes), the UI controlling circuitry 205 proceeds tostep S202.

Step S202 is a step implemented by the pixel shift amount calculatingcircuitry 222 included in the motion artifact correcting circuitry 220.At step S202, the pixel shift amount calculating circuitry 222calculates a shift amount by using the second image.

Step S203 is a step implemented by the re-sizing circuitry 225 includedin the motion artifact correcting circuitry 220. At step S203, there-sizing circuitry 225 calculates a correction value by multiplying theshift amount by the re-sizing coefficient.

Step S204 is a step implemented by the pixel shift amount applyingcircuitry 223 included in the motion artifact correcting circuitry 220.At step S204, the pixel shift amount applying circuitry 223 corrects thefirst image by using the correction value obtained from the secondimage.

As explained above, in the second embodiment, the resolution of thesecond photodetector 106 b is higher than that of the firstphotodetector 106 a. In other words, the second photodetector 106 b isable to more accurately calculate the pixel shift amount between themask image and the contrast image. Further, in the second embodiment,when the first image is to be displayed on the monitor 109, the X-rayimage acquirer 110 a calculates the shift amount by using the secondimage and further corrects the first image by using the calculated shiftamount. As a result, according to the second embodiment, for example, itis possible to provide a DSA image in which the motion artifact has beencorrected with a higher level of precision.

In the second embodiment above, the example is explained in which theX-ray image acquirer 110 a performs the process of correcting the motionartifacts, after the mask image and the contrast image are acquiredthrough the DSA manipulations; however, embodiments are not limited tothis example. For instance, the X-ray image acquirer 110 a may performthe process of correcting the motion artifacts in real time, every timea contrast image is acquired.

Embodiments are not limited to the embodiments described above.

In the embodiments above, the example is explained in which, asillustrated in FIG. 4 or FIG. 7, in the X-ray detector 106, the firstFED is provided on the X-ray source 103 side, relative to the secondFED; however, embodiments are not limited to this example. For instance,in the X-ray detector 106, the second FPD may be provided on the X-raysource 103 side, relative to the first FED.

Further, in the embodiments above, the example is explained in which theX-ray image acquirer 110 (or 110 a) includes the circuitry; however,embodiments are not limited to this example. For instance, anotherarrangement is acceptable in which the X-ray image acquirer 110 (or 110a) is a processor and, as a result of the processor reading andexecuting computer programs (hereinafter, “programs”) stored in storagecircuitry, the functions that are the same as those of the X-ray imageacquirer 110 illustrated in FIG. 4 or the X-ray image acquirer 110 aillustrated in FIG. 7 are executed. In that situation, the processingfunctions executed by the processor are recorded in the storagecircuitry in the form of computer-executable programs. The processorimplements the functions corresponding to the programs by reading theprograms from the storage circuitry and executing the read programs. Inother words, the processor that has read the programs has the functionsthat are the same as those of the circuitry illustrated within the X-rayimage acquirer 110 in FIG. 4 or within the X-ray image acquirer 110 a inFIG. 7.

The term “processor” used in the above explanation denotes, for example,a Central Processing Unit (CPU), a Graphics Processing Unit (GPU), or acircuit such as an Application Specific integrated Circuit (ASIC) or aprogrammable logic device (e.g., a Simple Programmable Logic Device[SPLD], a Complex Programmable Logic Device [CPLD], or a FieldProgrammable Gate Array [FPGA]). The processor implements the functionsthereof by reading the programs stored in the storage circuitry andexecuting the read programs. Instead of storing the programs into thestorage circuitry, it is also acceptable to directly incorporate theprograms into the circuit of the processor. In that situation, theprocessor implements the functions thereof by reading the programsincorporated in the circuit thereof and executing the read programs. Theprocessors disclosed in the embodiments do not each necessarily have tobe structured as a single circuit. It is also acceptable to structureone processor by combining together a plurality of independent circuitsso as to implement the functions thereof. Further, it is also acceptableto integrate two or more of the constituent elements illustrated in FIG.4 or FIG. 7 into one processor so as to implement the functions thereof.

In the explanation of the embodiments above, the constituent elements ofthe apparatuses and the devices illustrated in the drawings in theembodiments above are based on functional concepts. Thus, it is notnecessary to physically configure the constituent elements as indicatedin the drawings. In other words, the specific modes of distribution andintegration of the apparatuses and the devices are not limited to thoseillustrated in the drawings. It is acceptable to functionally orphysically distribute or integrate all or a part of the apparatuses andthe devices in any arbitrary units, depending on various loads and thestatus of use. Further, all or an arbitrary part of the processingfunctions performed by the apparatuses and the devices may beimplemented by a CPU and a computer program analyzed and executed by theCPU or may be implemented as hardware using wired logic.

It is possible to implement the controlling methods described in theembodiments above by causing a controlling program prepared in advanceto be executed by a computer such as a personal computer, a workstation,or the like. The controlling program may be distributed via a networksuch as the Internet. Further, the controlling program may be recordedonto a computer-readable recording medium such as a hard disk, aflexible disk (FD), a Compact Disk Read-Only Memory (CD-ROM), amagneto-optical (MO) disk, a Digital Versatile Disk (DVD), or the like,so as to be executed as being read from the recording medium by acomputer.

According to at least one aspect of the embodiments described above, itis possible to reduce the artifacts.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

What is claimed is:
 1. An X-ray diagnostic apparatus comprising: anX-ray detector including a first detector and a second detector capableof simultaneously detecting X-rays irradiated from an X-ray tube; andprocessing circuitry configured to correct, by using information of asecond image that is based on an output from the second detector, afirst image that is based on an output from the first detector.
 2. TheX-ray diagnostic apparatus according to claim 1, wherein the X-raydetector includes: a scintillator configured to convert an X-ray intolight; and a first photodetector and a second photodetector configuredto share the scintillator and detect light converted by thescintillator, the first detector includes the scintillator and the firstphotodetector, the second detector includes the scintillator and thesecond photodetector, and the first photodetector and the secondphotodetector simultaneously detect light converted from X-rays by thescintillator.
 3. The X-ray diagnostic apparatus according to claim 2,wherein the scintillator is arranged so as to be sandwiched between thefirst photodetector and the second photodetector.
 4. The X-raydiagnostic apparatus according to claim 2, wherein a residual componentresulting from incident X-ray of the second photodetector is smallerthan that of the first photodetector, and in a situation where anartifact due to the residual component occurs in the first image, whenan image displayed on a display is changed from the second image to thefirst image, the processing circuitry corrects the first image by usinga pixel value obtained from the second image.
 5. The X-ray diagnosticapparatus according to claim 4, wherein, when a difference between apixel value obtained by multiplying a pixel value of the second image bya coefficient corresponding to a sensitivity ratio between the firstphotodetector and the second photodetector and a pixel value of thefirst image is equal to or larger than a threshold value, the processingcircuitry determines that the artifact has occurred.
 6. The X-raydiagnostic apparatus according to claim 5, wherein a resolution of thesecond photodetector is higher than that of the first photodetector, andwhen comparing a pixel value of the first image with a pixel value ofthe second image, the processing circuitry corrects a pixel pitch of thesecond image.
 7. The X-ray diagnostic apparatus according to claim 4,wherein the processing circuitry calculates a correction value based ona pixel value obtained from the second image and a pixel value obtainedfrom the first image, and further corrects the first image bysubtracting the correction value from the pixel value obtained from thefirst image.
 8. The X-ray diagnostic apparatus according to claim 7,wherein the processing circuitry corrects at least one of a pixel valueobtained from the second image and a pixel value obtained from the firstimage corresponding to sensitivity of the first photodetector and thesecond photodetector, and further calculates a correction value bysubtracting a pixel value obtained from the corrected first image from apixel value obtained from the corrected second image.
 9. The X-raydiagnostic apparatus according to claim wherein a resolution of thesecond photodetector is higher than that of the first photodetector, andwhen the first image is to be displayed on a display, the processingcircuitry calculates a shift amount by using the second image andfurther corrects the first image by using the calculated shift amount.10. The X-ray diagnostic apparatus according to claim 9, wherein theprocessing circuitry calculates the shift amount by making a correctionby multiplying a pixel pitch of the second image by a coefficientcorresponding to a size of a field of view.
 11. The X-ray diagnosticapparatus according to claim 2, wherein a size of a field of view of thefirst photodetector is larger than that of the second photodetector.